1. Field of the Invention
This invention is generally related to auxiliary fuel tanks or pods for use with aircraft, primarily tactical or military aircraft, and particularly directed to expendable auxiliary fuel tanks or pods which are designed to be manually assembled in the field utilizing nestable and selectively assembled sections which are united or hingedly joined by continuously interlocking elements so as to enclose a flexible fuel retaining bladder therebetween. The tanks are braced by internal baffles which are cooperatively seated with the bladder. The design and multi-sectional structure of the fuel tanks enables the components for a plurality of tanks to be packaged and stored in high density configurations so that a plurality of tanks may be shipped in the same space heretobefore required for a single conventional auxiliary fuel tank. The fuel tank also provides structures which are quickly and manually assembled and aerodynamically sound without the need for numerous mechanical fasteners or complicated seals to insure tank and fuel storage integrity. The fuel tanks or pods are also provided with aircraft mounting strongbacks which are universally adaptable to permit a variety of fuel tank sizes and configurations to be readily fitted to a variety of aircraft and which strongbacks also include tank injection components thereby enabling the strongbacks to be used for a plurality of flight missions. The fuel tanks also include universally adaptable fuel exchangers and dispensing equipment.
2. History of the Prior Art
As discussed in applicant's prior application, Ser. No. 06/826,160 filed Feb. 4, 1986, now abandon, it has been an accepted practice to increase the flying range of aircraft and especially tactical jet aircraft by utilizing auxiliary fuel tanks or pods which are normally carried or mounted on the wings or fuselage tips of the aircraft. In some instances, the fuel pods are attached by means which allow the tanks to be selectively jetisoned by the pilot of the aircraft after the fuel therein has been expended.
The auxiliary fuel tanks are utilized during tactical mission operations to provide an initial fuel supply which enables an aircraft to reach a primary target area. At that point, most of the fuel in the tanks may be exhausted and the tanks readily jetisoned by the pilot. Thereafter, the aircraft is supplied with fuel from its primary fuel tanks.
Currently, the majority of expendable or external fuel tanks for military aircraft are manufactured and prepared for shipment to supply areas as individual relatively rigid units. These units are preassembled and include a welded aluminum tank which is integrally formed or attached to a strongback which connects the tank with the mounting mechanism or pylon on an aircraft. Aircraft fuel tanks are generally standardized in size and hold 150, 300, 600 or more gallons of fuel. Such tanks may be 12-15 feet in length and approximately two or more feet in diameter. As most conventional expendable auxiliary fuel pods are preassembled and shipped to the military as a unit, the size and shape of the fuel tanks not only makes the physical handling thereof more difficult but also requires a considerable amount of storage area be set aside to store tanks for subsequent use on tactical aircraft. The amount of storage space becomes a matter of particular concern when considering that such fuel tanks may be stored on aircraft carriers o in other areas such as in forward line depots wherein a limited amount of space is available.
In addition to the foregoing, conventional external or auxiliary fuel tanks for aircraft are designed and constructed in such a manner as to insure the integrity of the outer casing or shell to prevent any leakage of fuel therefrom and to also insure that the pressures both interiorly and exteriorly of the tank will not cause any failure or fatigue in the shell. As the aerodynamic stresses to which such tanks are subjected may often be considerable especially when such fuel pods are used on mach 1 and mach 2 jet aircraft, it is imperative that the overall tank structures be sound and be capable of withstanding the stresses imparted thereto during situations of power dives, climbs and turns as well as impacts from flying objects. To this end, conventional tanks are solidly constructed so as to withstand such impacts and stresses. This increases the overall cost and weight of the tanks and results in relatively rigid tank structures.
The drawbacks with respect to conventional auxiliary fuel pods or tanks for aircraft is increased when considering the expendable nature of such tanks. As one aircraft can make several mission flights during a very short period of time, it is possible that numerable tanks will be utilized by a single aircraft. Therefore, a great deal of storage area must be set aside to provide the space for storing fuel tanks for a single aircraft.
It has been proposed to construct fuel pods in sections wherein the sections may be assembled at a forward field area to thereby reduce the amount of storage space required for such tanks. In this regard, a number of patents have been directed to various configurations for auxiliary fuel tank constructions which enable the tanks to be broken down into parts for shipment and storage. Unfortunately, it has not been found practical to utilize the structures disclosed heretobefore for any of a number of reasons. In some instances, the integrity of such sectionalized fuel tanks has not permitted their use in actual field operations. In other instances, the structures have been too complex or complicated to be easily assembled in the field thereby making their use uneconomical both in cost and time.
In U.S. Pat. No. 2,545,481 to Maier, an expendable fuel tank is disclosed having upper and lower sections which are nestable so that a number of tanks can be stored within one another. One drawback of the structure disclosed is that the upper and lower sections are different in shape and structure and therefore are not interchangeable with respect to one another thereby requiring that the upper halves and the lower halves be matched for each assembly. Also, the upper and lower sections provided only a limited stacking capability as the mounting portion of the upper half of the fuel pods interfere with the components as they are stacked or nested with respect to one another.
Other examples of prior art sectionalized auxiliary expendable fuel tanks are disclosed in U.S. Pat. Nos. 2,661,115 to Fletcher and 2,863,583 to Trump. In the Trump structure, the tanks are sectionalized between their fore and aft sections having separately nestable forward sections and separately nestable aft sections. The forward and aft sections are assembled over a frame which is provided for rigidity and which is assembled prior to placing the sections of tanks in mounted relationship with respect thereto. In Fletcher, the aft sections are stored within the forward sections. Not only does the splitting of the housing into forward and aft sections create problems with additional storage space as the sections do not nest or stack uniformly so that sections must be separately stacked or housed with respect to one another but such structures require numerous complicated connectors and seals to unite the sections in tightly fitted engagement. Also, additional storage space must be provided to ship and store the frame members which constitute the central reinforcing portion of such fuel pod systems.
In an effort to improve the compact storage of forward and aft sectional fuel tanks, unique packaging components have been designed to house a plurality of fuel tanks. In U.S. Pat. No. 3,469,730 to Neff et al., a packaging structure is disclosed wherein four sectionalized tanks are nestable within a tubular carrier. Although the increased storage capacity of the structure offers advantages over prior sectionalized tanks, the structure remains overly complicated and not conducive for use in rapid assembly operations.
As mentioned above, another problem associated with previously proposed sectionalized auxiliary fuel tanks is that the integrity of the outer portion of the tanks must be sound to prevent any leakage of fuel even when stresses are imparted to the tank during flight. Therefore, special rubber or other gasketing is provided between the sections of the tanks in order to seal the same when assembled. Unfortunately, the placement of the seals is too exacting a task and very time consuming. In exact tolerances may result in limited amounts of leakage through the sealed joints and, in some instances, the aircraft fuel supply may be adversely effected by air entering the tanks through the sealed joints. Further, the cost for machined parts which must be assembled in a leak-proof manner makes the multipart construction of the aforementioned proposed prior art devices as costly as the preassembled construction currently being utilized by the military. Also such structures are not easily assembled using interchangeable components and require specialized tools and/or handling equipment.
Additional examples of prior art sectionalized expendable fuel tanks are disclosed in U.S. Pat. Nos. 2,756,893 to Barrere, 2,781,935 to Spieth et al., 2,895,635 to Pallard et al. and 4,113,130 to Lazenby et al. In the Barrere patent, the seal of the tank is provided by a pneumatic tube which is disposed between the jointed members The use of such a pneumatic seal could very easily lead to fuel leakage especially when considering the various pressures to which the tank would be exposed to during actual flight operations. U.S. Pat. No. 2,876,923, to McLane et al. discloses the use of an elastomeric sealing ring which is placed between fore and aft sections of a multi-sectioned auxiliary fuel tank. As with the prior patents discussed above, the tolerances which must be met in order to insure that there is no leakage through the sealed joints will result in a fuel tank which would be more expensive to manufacture and deliver than the preassembled units currently being used. In the remaining structures, special joints and seals for assembling and reinforcing tank sections are disclosed. Again, such structures are overly complex, not capable of rapid assembly by non-skilled personnel and are not readily stackable for compact packaging, shipment and storage.
Sectionalized fuel tanks currently in inventory consist of many form-fitting components that must be connected and secured with precision. The assembly of plumbing, gauges and baffles is an extremely complex and tedious operation. The precise alignment of bolt holes can complicate and delay assembly. After considerable time and effort is expended uncrating and assembling tanks, a significant number fail to pass required pressure and leak tests. This results in additional time and manpower being devoted in determining the source of the malfunctions and making the necessary repairs These problems in assembly cause users to elect to incur additional logistics burdens and have tanks shipped fully assembled from the manufacturer.
Also, to prepare such tanks for operational use requires a complex set of assembly instructions which often must be interpreted by relatively unskilled personnel. Another factor essential to assembly is that all required parts have been included in packaging and are not defective either from the manufacturing process or damage resulting from shipment. Present tanks are designed to be put together in periods of hours. The result, the assembly process is not time effective.
In view of the foregoing, the prior art has not fully appreciated the need to develop easily assembled sectionalized auxiliary fuel tanks for military aircraft which not only offer high density packaging and storage but also provide for safe and reliable fuel storage structures without complex seals and interlocking components. Although the prior art appreciates that some stacking of components could be possible, with the structures designed to date, only limited stacking would be possible permitting maybe four to perhaps eight units, at most, to be stacked, shipped or stored within the space required by a conventional single piece or preassembled tank. With the additional costs required for securing sectionalized tanks in assembled relationship including insuring that the joints are leakproof, prior art sectionalized fuel pods have not been adequate nor acceptable for use in the field.
Additionally, conventional external tanks are specifically designed to function as a predetermined integral unit capable of functioning properly within given flight conditions, fuel capacities and with specific aircraft. If designed for 150 gallan capacity and subsonic flight, then this becomes a tank's established profile. If the tanks have been designed for limited maneuvering and certain pressures and stresses, then these are the limiting use factors for the tanks. Once a tank is manufactured, its performance profile is set and remains inflexible for the life of the hardware. For this reason, each military service maintains a number of fuel tanks, each designed for a specific purpose and aircraft. The tanks normally range anywhere from 150-650 gallons and are structured for a variety of flight conditions. If several major components of these tanks were interchangeable, a number of tank designs would become available to a variety of aircraft in inventory. The immediate benefit would be a substantial reduction in the total number of fuel tank components that would be required to stock and maintain in inventory.